The present invention relates to a catalytic combustion burner made of porous material, comprising in its lower part an substantially axial cavity for receiving a wick designed to convey a combustible liquid to the burner, and in its upper part an annular peripheral zone carrying a catalyst and surrounding a central zone with no catalyst forming a vaporising zone.
By way of example such a burner was described in patent FR-B-2 610 390 in the name of the present applicant.
The combustible liquid conveyed by the wick penetrates into the pores of the burner""s porous material. Some of this liquid reaches the annular peripheral zone with the catalyst and there undergoes catalytic combustion, which keeps this peripheral zone at a high temperature.
Another part of this liquid passes through the central zone of the burner and is vaporised there.
It is recommended that combustible liquid be regularly topped up in a flask equipped such a kind of burner. However, experience shows that many users forget to turn off the burner and leave it alight until the combustible liquid is entirely used up.
When there is no more combustible liquid in the flask, the wick dries out, and its upper end, trapped in the upper part of the burner cavity, and being in contact with its hot walls, tends to burn in the absence of oxygen and to carbonise, producing free particles of carbon which in turn block up the pores of the burner. The same thing occurs with the last usable amounts of the combustible liquid conveyed at a decreasing rate by the wick, which no longer pass through the walls of the burner and the incomplete combustion of which likewise frees amorphous carbon particles. As a result the efficiency of the burner is reduced, it becomes unusable and it has to be chanqed.
FR-B-2 483 782 and FR-A-2 530 144, in the applicant""s name, describe a burner in the form of an annular catalytic disk made of inert materials into which is mixed a catalyst. This disk has an axial hole through it into which a skirt is inserted, which reaches as far as a tubular wick and contains no catalyst. The upper part of the tubular wick surrounds the skirt under the annular disk. There is a second wick inside the tubular wick, inserted inside the skirt.
No burner of this kind has ever gone beyond prototype stage, partly because of its complexity, and partly because the two wicks tend to carbonise rapidly in contact with the hot annular catalytic disk.
The purpose of the invention is to overcome the drawbacks of the problems relating to the catalytic combustion burner of the aforementioned type and to put forward a burner of the same type where there is no risk of the wick carbonising, even if a user forgets to turn off the burner and leaves it alight until the combustible liquid contained in the flask is completely used up.
In the present invention, the particular feature of the catalytic combustion burner of the aforementioned type is that it has in its upper part at least one open channel enabling the upper part of the cavity to communicate with the atmosphere.
The open channel enables oxygen to be fed continuously into the upper part of the cavity. Once the combustible liquid has been entirely used up, the dried out wick therefore, in contact with the walls of the burner, should the latter be too hot, burns the constituents of the wick completely along with the last amounts of combustible liquid, producing CO2 and H2O in gas form. This prevents the production of carbon particles, which might block the burner""s pores.
Furthermore, fresh air can arrive via the channel, accelerating cooling of the cavity interior walls, such that wick combustion ends earlier than in the previous situation.
In contrast to the case of the above-mentioned annular catalytic disc burner, where the coaxial wicks carbonised rapidly in contact with the walls of the annular disc despite the presence of the axial hole containing the central wick, the open channel, because it provides for communication between the upper part of the cavity and the atmosphere, is sufficient, even if its diameter is small in comparison with that of the cavity, for carbonisation to be avoided.
As a result, it is possible to leave the burner alight until all the combustible liquid in the flask with said burner is consumed without risk of damaging said burner.
In one advantageous version of the invention, said channel is substantially axial and preferably has a diameter of substantially a quarter to a half of the diameter of the cavity.
Another aspect of the invention also relates to a catalytic combustion flask, suitable for containing combustible liquid, the neck of which holds a catalytic combustion burner with a wick dipping into said liquid.
In this invention, this flask is characterized in that it is equipped with a burner in accordance with the first aspect of the invention.
Other particular features and advantages of the present invention will become apparent in the detailed description hereinbelow.